Burn-out time data analysis on interaction effects among multiple fires in fire arrays

Abstract

This paper gives an experimental and methodological investigation on the behaviors of square fire arrays which are composed of 3 × 3 to 7 × 7 n-heptane fires initiated from fuel pans of 5 cm in diameter and 2 cm in height. It is intended to develop a burn-out time (BOT) data analysis method to analyze the interaction effects (which may induce fire merging and fire whirls) among the multiple fires. In 26 fire tests the fire point spacing D varied from 20 to 50 cm for each array size and in several cases shear flow was added from one side of the array. By considering the flame height L a reasonable critical condition for initiation of fire merging was implied to be D/ L = 0.29 − 0.34, which is independent of the fire array size and fire point spacing. By burn-out time data the Interaction index I ( m) and Interaction link index A ( m, n) were defined to characterize the fire interactions. The assumptions essential to solve the equation system of I ( m) = ∑ n A ( n, m) were examined in detail, whereby the equation system was solved. The analysis showed that the burn-out time data analysis realizes a quantitatively reasonable comparison of the fire interaction effects, thus indicating that it is reasonable to regard the burn-out time as a measure for the average burning rate for each specific fire point. An apparent criterion of BOT( m)/BOTR = 0.5 was summarized to identify whether any fire point m will be completely involved in fire merging (where BOTR is the burn-out time of the free burning reference fire point). It was implied that the interaction effect imposed on any fire is mainly ascribed to its adjacent four fires. The effects of shear flow to fire burning and occurrences of fire whirls were also discussed.